1. Field of the Invention
The present invention relates to a burn-in apparatus which can operate a semiconductor integrated circuit including a microcomputer, e.g., an electronic control unit for automobile (referred to as "ECU" hereinafter) in an on-board condition (i.e., a condition where the circuit is mounted on a substrate) at high temperature and high voltage.
2. Description of the Prior Art
Usually a semiconductor integrated circuit such as ECU for automobile is subjected to "screening" so as to remove its early failure. Where "screening" consists of "burn-in" and "test", and the term "burn-in" means to operate the circuit at high temperature and high voltage and the term "test" means to check based on the result of burn-in whether the circuit is defective or not.
In the prior art, the semiconductor integrated circuit such as ECU for automobile has been subjected to screening to pick out early failure beforehand after a chip has been assembled into a package. However, in recent years, trials such as a bare ECU has been made wherein the semiconductor integrated circuit is mounted in a bare chip state to reduce a size of the substrate and to miniaturize the ECU, etc.
As described above, a technology that the burn-in voltage is supplied to conduct screening after the semiconductor integrated circuit is mounted on the substrate has been disclosed in Japanese Patent Application Publication (KOKAI) 7-287603. In this prior art, in the screening operation, the power supply voltage output of the stabilized power supply circuit in the ECU mounted on the substrate is switched to the higher voltage than the normal voltage according to the signal which is supplied from the external stabilized power supply voltage switching signal generator.
However, in the above prior art, since the power supply voltage output of the stabilized power supply circuit mounted on the substrate is switched to the higher voltage than the normal voltage according to the signal supplied from the external stabilized power supply voltage switching signal generator in the burn-in operation, a connector terminal which is not used in actual operations must be provided to the ECU connector for automobile to thus render the burn-in apparatus expensive. In addition, there has been no disclosure of the circuit configuration of the stabilized power supply circuit which switches the power supply output into the specified burn-in voltage being higher than the normal power supply voltage in the burn-in operation. Therefore, it is not apparent what circuit switching would be executed to generate a specified burn-in voltage and how the screening operation of the semiconductor integrated circuit which is mounted on the substrate as the bare chip would be executed by making use of such specified burn-in voltage.